1. Field of the Invention
This invention relates to adhesion promoting additives for curable organosiloxane compositions. More particularly, this invention relates to additives that impart excellent adhesion to organosiloxane compositions. The additives are especially useful for organosiloxane compositions that cure by a platinum-catalyzed hydrosilation reaction at temperatures up to 100.degree. C. and composition that cure upon irradiation with ultra-violet light.
2. Background Information
Adhesion additives for curable organosiloxane compositions are organosilicon compounds that typically contain at least two functional groups.
U.S. Pat. No. 3,772,026 and U.S. Pat. No. 3,873,334 describe acyloxy functional silanes which additionally have silicon hydride or alkenyl functionality respectively. Although the acyloxy functionality is very reactive, it liberates corrosive acetic acid upon reaction with hydroxyl groups present at the surface of the substrate or with water ingressing into the composition.
U.S. Pat. No. 4,196,273 discloses unsaturated alkoxysilanes as adhesion additives, however, adhesion is not demonstrated at temperatures below 100.degree. C. and only adhesion to glass is demonstrated at 100.degree. C.
U.S. Pat. No. 4,329,273 teaches using partial hydrolyzates of unsaturated alkoxysilane. Compositions containing these adhesion additives cured at 100.degree. C. but not at ambient laboratory temperatures.
U.S. Pat. No. 4,082,726 describes adhesion promoters that are organosilicon compounds containing epoxy functional dialkoxysilyl groups and at least one alkenyl group or hydrogen atom bonded to silicon in the organosilicon compound. Adhesion is demonstrated after curing at temperatures between 100.degree. and 200.degree. C.
U.S. Pat. No. 4,087,585 teaches physical blends of epoxy functional alkoxysilanes with silanol functional fluids containing alkenyl functionality. The compositions were cured at temperatures below 150.degree. C. for elastomer compositions whose adhesion was measured.
Organosilanes containing ethylenic unsaturation, epoxy functionality, and alkoxy functionality are taught in U.S. Pat. No. 4,732,932.
U.S. Pat. No. 5,106,933 uses at least two of the following compounds as adhesion promoters: organosilicon compounds containing at least one (meth)acryloxyalkyl or epoxy group and at least two silicon-bonded alkoxy groups and isocyanurate compounds.
U.S. Pat. No. 4,659,851, U.S. Pat. No. 4,719,262, and U.S. Pat. No. 4,906,686 each teach reaction products of unsaturated alcohols with alkoxysilanes. However, the resultant Si--O--C bond between the unsaturated alcohol and alkoxysilane would be susceptible to hydrolysis, with the result that adhesion may be substantially decreased upon exposure to moisture.
U.S. Pat. No. 4,077,943 teaches use of a silicon hydride crosslinker which additionally contains epoxy functionality.
U.S. Pat. No. 4,786,701 teaches adhesion promoters which are hydrolysis reaction products of tetraalkoxysilanes, alkenyl or silicon hydride functional organopolysiloxanes, and optional (meth)acryloxy functional alkoxysilanes.
U.S. Pat. No. 4,677,161 teaches silicon hydride functional SiO.sub.2 resins containing residual OR functionality, but no Si(OR).sub.3 functional groups are present.
None of the aforementioned patents demonstrate adhesion at temperatures below 100.degree. C. or adhesion to a variety of substrates.
European Published Application 449,181 describes organohydrogensiloxanes containing at least two silicon-bonded hydrogen atoms and at least one trialkoxysilyl group. Organosiloxane compositions containing this compound exhibited adhesion after curing at temperatures between 120.degree.-150.degree. C.
Japanese Laid Open Pat. Application (JLOPA) 4/311,766 teaches adhesion promoting additives containing a) siloxane units with at least one alkoxysilylalkyl group, b) siloxane units with at least one terminally unsaturated alkenyl radical; c) trialkoxysiloxy units and d) SiO.sub. 4/2 units. JLOPA 1/085,224 teaches accelerating the development of adhesion using organosiloxanes containing epoxy functional silsesquioxane units and optional ethylenic unsaturation, but no Si(OR).sub.3 functional groups. JLOPA 2/18452 describes adhesion promoters that include organosilicon compounds containing two silicon-bonded alkoxy groups and at least one epoxy group and organosilicon compounds containing at least one alkoxy group and at least two ethylenically unsaturated double bonds per molecule. JLOPA 1/085,224 teaches adhesion accelerators based on epoxy functional silsesquioxane units, optionally containing unsaturation, but no Si(OR).sub.3 functional groups.
U.S. Pat. No. 4,912,188 teaches linear organosilicon compounds containing olefinically unsaturated hydrocarbons, epoxy functionality, and optional alkoxy functionality at the terminus of the silicon compound. Compositions containing these compounds did not cure after 24 hours at room temperature. Adhesion was demonstrated after cure at 150.degree. C.
U.S. Pat. No. 4,721,764 teaches organopolysiloxanes containing two silicon bonded hydrogen atoms and at least one silicon bonded hydrolyzable group or oxirane group.
U.S Pat. No. 5,232,959 describes curable organosiloxanes containing as the curing agent an organohydrogenpolysiloxane comprising a linear sequence of at least five silicon atoms. Each molecule of this organohydrogensiloxane contains at least three silicon-bonded hydrogen atoms, at least one epoxy group, and at least one trialkoxysilyl alkyl group. The organohydrogenpolysiloxane is the sole curing agent and therefore forces limitations in formulation latitude. None of these patents demonstrate adhesion at temperatures below 120.degree. C.
European Published Application 469,890 teaches organopolysiloxane compositions wherein at least one of the alkenyl or organohydrogenpolysiloxanes contains at least two alkoxy groups and/or at least one epoxy group in the molecule. The cured products were gels which were cured between 80.degree.-150.degree. C. Gels are known to have self adherent properties.
One objective of this invention is to provide additives for organosiloxane compositions that impart excellent adhesion to substrates that are in contact with the compositions during curing. The additives are particularly useful in compositions that cure by a hydrosilation reaction at temperatures up to 100.degree. C.